In general, a canned motor pump is cooled at its motor part and lubricated at its bearings by circulating a portion of the treating fluid through a rotor chamber of the canned motor. However, in a canned motor pump for treating a fluid of more than 200.degree. C., the motor is obviously difficult to cool directly with fluid of such temperature, necessitating a separate cooling system, for example, a separate cooling water supply. For this reason, such type of canned motor has the disadvantage of a high initial cost because of the additional requirements for a separate cooling system in addition to the pumping system. Further, a conventional canned motor pump is unsatisfactory as regards conservation of natural resources or energy because of the heat loss due to cooling and additionally suffers from the disadvantage of entailing an extreme1y high fuel cost for a heating source for the high temperature fluid.
Now it has been found that the heat load for the treating source for the high temperature fluid may be significantly reduced by constructing a canned motor in a thermal resistant structure in which the canned motor is connected to the pump via an adapter, in which the thermal resistance of a bearing liquid seal is enhanced and in which heat values generated by the motor are absorbed into the circulating fluid.
While the improvement in the heat resistance of motor components is necessary for enhancing that of the canned motor itself, the dielectric strength of the winding at high temperature is especially important. The conventional canned motor, as generally constructed, has an insulation for insulating a set of windings, which thermally deteriorates in a high temperature environment of more than 200.degree. C., leading to poor mechanical strength and damage to the windings.
In this respect, we have found that the mechanical and the dielectric strength of the winding may be increased by using, as the insulation for the winding, an insulation formed in such a way that synthetic fluorinated mica pieces together with an organic solvent are suspended in an organic silicone solvent and the resulting material is impregnated and cured. Such type of insulation will vaporize some fluorine compunds from the synthetic fluorinated mica in a high temperature environment of more than 200.degree. C., and these compounds will react with siloxane derived from the organic silicone compound for ceramicization, thereby increasing the mechanical and dielectric strength of the winding.
Still further it has been found that the heat values from the motor may be absorbed in the treating fluid for maintaining the latter at the desired high temperatures above 200.degree. C. by constructing the canned motor pump in such a way that the canned motor with enhanced heat resistance is connected to the pump through the intermediary of an adapter for thermally separating the motor. For cooling the motor a portion of the high temperature treating fluid is circulated into the canned motor partially through external piping in which the high temperature fluid is cooled in an ambient environment for providing a desired temperature reduction, the resulting temperature difference of the treating fluid enabling natural circulation of the fluid or, if desired, an auxiliary impeller may forcibly circulate the same into the canned motor. Thus, a canned motor pump for use at high temperature of simple construction may be obtained, which contributes to conservation of natural resources and energy, thereby significantly reducing operational costs.